The present invention relates to an alternator for vehicles, and more particularly to an alternator for vehicles, provided with a voltage regulator suitable as a generator for automobiles.
The following has been demanded of conventional alternators for vehicles. First, in order to cope with an increase in electric load on a vehicle, high output and miniaturization have been demanded of alternators for vehicles. Second, reduction in noise has been demanded of alternators for vehicles.
While a field coil, a stator, a voltage regulator and a rectifier involve generation of heat during operation, each of them has to be kept at or below a certain temperature in order to preserve its capacity. Most alternators for vehicles, according to the prior art, are of air cooling type, in which a cooling air is used to cool respective parts thereof. When alternators for vehicles are adapted for high output, amounts of heat generated in a stator, a voltage regulator, a rectifier and so forth will increase. Also, with further miniaturization, a heat radiating area decreases and hence respective parts become liable to rise in temperature. Therefore, there is caused the need of enhancing the cooling performance for respective parts in an alternator.
Conceivable ways to enhance the cooling performance include an increase in flow rate of a cooling air since air flows are presently used for that purpose. Thus, a large-sized fan or a plurality of fans for synchronization with a rotor are mounted to generate flows of cooling air for cooling a field coil, a stator, a voltage regulator, a rectifier and so forth. Apart from that, there is a way to use a coolant to enhance the cooling performance of an alternator for vehicles. The use of a coolant eliminates the necessity of a fan or fans used in an air cooling system, and is greatly effective in reduction of noise.
There is a way to use as one of such coolants a cooling water for an engine. A prior water cooling system for alternators for vehicles is disclosed in Japanese Patent Unexamined Publication No. 11-243658. In this prior system, a plurality of rings (hereinafter, referred to as rotary disks) are provided on both axial sides of a rotor to have a certain height and be concentric with an axis of a rotating shaft. A plurality of rings (hereinafter, referred to as stationary disks) having a certain height and concentric with the axis of the rotating shaft like the rotary disks are provided on inner surfaces of a front bracket and a rear bracket to face opposite surfaces of the rotary disks and mesh with the rotary disks with a certain air gap. Therefore, when the rotating shaft rotates, the rotor rotates together therewith, and the rotary disks rotate in the same manner. As the rotary disks then rotate keeping some air gaps between them and the stationary disks, they can rotate without coming into contact with the stationary disks. Heat generated by a field coil can be transmitted to the rotor, the rotary disks, the air gaps, the stationary disks, the front bracket, the rear bracket and a cooling water in this order to define a thermal path, so that heat of the field coil is radiated to the cooling water.
A prior technique associated with a cooling means for a stator in a motor for vehicles is disclosed in Japanese Patent Unexamined Publication No. 2000-116062. In this technique, the motor for vehicles consists of a motor, a casing and a housing. A passage, through which a running air flow passes, is formed between the casing and the housing, and a surface of the casing in contact with the stator of the motor is provided with partition plates, radiating fins, turbulent flow producing projections to enhance the efficiency of heat exchange with the running air flow.
The following issues have remained in the above prior art. In order for an alternator for vehicles to develop an adequate output in operation, it is essential to flow a field current adequately. However, when current flows through the field coil, the internal resistance of the field coil causes the field coil itself to generate heat. Once the field coil generates heat to rise in temperature, the internal resistance of the field coil further increases to lead to insufficient field and no acquisition of output. Therefore, cooling of the field coil is essential. Further, in order to restrain degradation, in the performance of a motor for vehicles, caused by temperature rise, it is necessary to efficiently cool the stator coil.
With an arrangement disclosed in Japanese Patent Unexamined Publication No. 11-243658, the cooling performance is dominantly effective between the rotary disks and the stationary disks in the heat radiation path for cooling the field coil. This is because heat is transferred mainly by conduction from the rotary disks to the stationary disks via air gaps having a lower thermal conductivity than that of metal or the like. Therefore, in order to enhance the cooling performance, it is necessary to decrease the gaps between the rotary disks and the stationary disks or to increase heat transfer areas of respective disks. However, in view of accuracy of machining and quality of assembly, the gaps are practically around 1 mm. Therefore, for enhancement of the cooling performance, there is caused a problem that there has been a problem a multiple ring structure capable of being increased in heat transfer area is adopted to be increased in costs of machining, parts and assembly.
Also, with an arrangement disclosed in Japanese Patent Unexamined Publication No. 2000-116062, the rate of heat exchange with a running air flow is enhanced and a stator coil is cooled by providing heat radiating fins, turbulence generating projections and the like on a surface of a casing in contact with the stator. However, a rotor is not enhanced in cooling performance, which rotor is designed to be mounted in a space substantially enclosed by the casing. In the case where this technique is applied to an alternator for vehicles, a stator coil is cooled but a rotor is not fully cooled, resulting in an increase in internal resistance of a field coil to lead to no enforcement of adequate field, so that output cannot be obtained adequately.
An object of the present invention is to provide an alternator for vehicles, capable of enhancing the cooling performance of a field coil to develop an adequate output during power generation even if a gap between a rotor surface and a heat transfer surface, to which heat of a rotor is transferred, is large, and reducing costs of machining, part cost and cost of assembly.
The above-described object can be attained by an alternator for vehicles, which comprises a stator comprising a stator core and a stator coil wound around the stator core; a rotor comprising a rotating shaft, a magnetic pole core fitted onto the rotating shaft, and a field coil for magnetizing the magnetic pole core; a rectifier provided on a bracket, which receives therein the rotor; a voltage regulator for regulating the exciting voltage on the field coil; bearings provided on the bracket to support the rotating shaft; and turbulent flow generating members provided in a space closed by surfaces of the rotor and heat transfer surfaces, to which heat is transferred from the rotor, to generate a turbulent flow.
Also, the alternator for vehicles may be of a liquid-cooled type, in which coolant flow passages are provided on a housing around the stator or on the bracket supporting the rotor through the bearing.
Further, concretely, the turbulent flow generating member comprise one or a plurality of members having recesses or projections. They may be made of a metal such as iron or aluminum, resin or sintered material. These turbulent flow generating members generate turbulence in a flow in the closed space to adequately stir the liquid, so that heat transfer over the surface of the rotor and the heat transfer surface of the bracket is enhanced and passing of heat between them is promoted.
Other features, objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings.